GLITP optical monitoring of QSO 0957+561: VR light curves and variability     

A. Ullán  L. J. Goicoechea  J. A. Muñoz  E. Mediavilla  M. Serra-Ricart  E. Puga  D. Alcalde  A. Oscoz  R. Barrena 《Monthly notices of the Royal Astronomical Society》2003,346(2):415-423

The Gravitational Lenses International Time Project (GLITP) collaboration observed the first gravitational lens system (QSO 0957+561) from 2000 February 3 to March 31. The daily VR observations were made with the 2.56-m Nordic Optical Telescope at Roque de los Muchachos Observatory, La Palma, Spain. We have derived detailed and robust VR light curves of the two components Q0957+561A and Q0957+561B. In spite of the excellent sampling rate, we have not found evidence in favour of true daily variability. With respect to variability on time-scales of several weeks, we measure VR gradients of about −0.8 mmag d⁻¹ in Q0957+561A and +0.3 mmag d⁻¹ in Q0957+561B. The gradients are very probably originated in the far source. Thus, adopting this reasonable hypothesis (intrinsic variability), we compare them to the expected gradients during the evolution of a compact supernova remnant at the redshift of the source quasar. The starburst scenario is roughly consistent with some former events, but the new gradients do not seem to be caused by supernova remnant activity.  相似文献   

Geochemical characterization of the salinity of irrigated soils in arid regions (Biskra,SE Algeria)     

Abdennour  Mohamed Amine  Douaoui  Abdelkader  Barrena  Jesús  Pulido  Manuel  Bradaï  Abdelhamid  Bennacer  Amel  Piccini  Chiara  Alfonso-Torreño  Alberto 《中国地球化学学报》2021,40(2):234-250

Acta Geochimica - The agriculture in Biskra, southeastern Algeria, is based on traditional practices and characterized by small irrigated fields. In the last decades, the increasing demand in water...  相似文献   

A study of the behaviour of the Na i/K i column density ratio in the interstellar medium using the Na ultraviolet doublet     

S. N. Kemp  B. Bates  J. E. Beckman  C. J. Killow  R. Barrena  D. C. Kennedy  J. Rodríguez Alamo 《Monthly notices of the Royal Astronomical Society》2002,333(3):561-574

Here we make a new study of the behaviour of the Na  i /K  i column density ratio in the interstellar medium, using a sample of new observations of 28 stars obtained at the Nordic Optical Telescope (NOT) in 1996 and 1997, and previously published observations (obtained by some of the authors) of 21 stars. The sightlines cover a range of distances and directions, including into the Galactic halo. We make use of new observations of the Na  i ultraviolet (UV) doublet for some 18 stars. This doublet is much weaker than the Na  i D doublet and so is less susceptible to saturation effects, and it is well known that it can be used to obtain more accurate Na  i column densities with a smaller error range. We find an average N (Na  i )/ N (K  i ) ratio from the Na  i UV data of about 90, which is rather higher than that found previously by Hobbs and Lequeux. The Na  UV–K  i   ratio shows a small increase in value with increasing column density, while we also find a sample of low N (Na  i )/ N (K  i ) ratio clouds generally seen towards distant objects on high-latitude sightlines that reach into the halo, so that the ratio decreases more sharply at lower column densities. As the values of the ratio for these halo clouds  (10–20)  bracket the cosmic Na/K abundance ratio, we suggest that these ratios result from a harder radiation field in the lower halo, such that the ionized fractions of Na  i and K  i become similar. Clearly caution needs to be applied in using any kind of 'standard value' for the Na  i /K  i column density ratio.  相似文献